Methods of using stable hydrocarbon foams

ABSTRACT

A method of treating a subterranean geological formation comprising hydrocarbons comprising injecting a foam into the formation at a rate and pressure sufficient to open at least one fracture therein and a method of completing a well in a subterranean geological formation penetrated by a well bore comprising introducing a foam into the well bore of the subterranean geological formation and carrying out a completion operation in the well bore of the subterranean geological formation. The foam comprises a liquid hydrocarbon and a nonionic polymeric surfactant comprising fluorinated repeating units, wherein the fluorinated repeating units have up to 5 perfluorinated carbon atoms, and wherein a one weight percent solution of the nonionic polymeric surfactant in kerosene has a foam half-life at 22° C. of at least 10 minutes.

BACKGROUND

Fracturing a hydrocarbon-producing well (e.g., an oil or natural gas well) is a common technique designed to increase the productivity of the well by creating highly conductive fractures or channels in the hydrocarbon-producing geological formation around the well. Such fracturing is usually accomplished by injecting a fluid at a high rate and high pressure to create fractures (i.e., hydraulic fracturing).

Various operations (e.g., cleaning the well bore, gravel packing the well, and cementing the well), often referred to as completion operations, are used to prepare a hydrocarbon-producing well for production. Fluids used in the completion operations are commonly called completion fluids.

The use of foamed fluids in fracturing or completion operations is known. Foamed fluids may have several advantages over non-foamed fluids. For example, the volume of liquid in a foamed fluid is less than in non-foamed fluids, and as a result, less fluid loss to permeable subterranean formations occurs when a foam is used. Further, foamed fluids are typically more easily removed from a geological formation following a fracturing or completion operation than non-foamed fluids. Foamed fluids (including either gelled or non-gelled fluids) also tend to have a greater ability than their non-foamed counterparts to suspend and transport particulate materials (e.g., proppants, gravel, and released fines) that are used or produced in fracturing or completion operations.

Liquids utilized as the liquid phase in foams employed in fracturing or completion operations include water, hydrocarbons, and aqueous alcohol solutions. The use of one or more hydrocarbons in the liquid phase of foamed fluids for subterranean formation treatments is advantageous when the subterranean formation is sensitive to the intrusion of water foreign to the formation. Such water-sensitive formations generally contain clays that are irreparably damaged upon foreign water contact due to the swelling of the clays and/or the migration of fines as a result thereof.

In a foam, gas bubbles are separated from each other by thin liquid films. Typically, surfactants stabilize foams by adsorbing at the interface of the bubbles and the liquid films and providing a barrier to coalescence of the bubbles. It is typically more challenging to form hydrocarbon foams than to form aqueous foams. Unlike water, which has a high surface tension and can dissolve charged species, hydrocarbons generally do not have properties that prevent the coalescence of gas bubbles.

Some fluorinated surfactants are known to produce stable hydrocarbon foams. Traditionally, many of the widely available fluorinated surfactants include long-chain perfluoroalkyl groups, for example, perfluorooctanesulfonamido groups. Recently, however, there has been an industry trend away from using perfluorooctyl fluorinated surfactants, which has resulted in a need, for example, for new types of surfactants that can produce hydrocarbon foams.

One nonionic polymeric fluorinated surfactant having perfluorobutanesulfonamido-containing repeating units and a weight average molecular weight of about 15,000 grams per mole has been used as a hydrocarbon foaming agent in drilling fluids and in enhanced oil recovery fluids added to injection wells.

SUMMARY

In one aspect, the present invention provides a method of treating a subterranean geological formation bearing hydrocarbons, the method comprising:

injecting a foam into a subterranean geological formation bearing hydrocarbons at a rate and pressure sufficient to open at least one fracture therein, wherein the foam comprises a liquid hydrocarbon and a nonionic polymeric surfactant comprising fluorinated repeating units, wherein the fluorinated repeating units have up to 5 perfluorinated carbon atoms, and wherein a one weight percent solution of the nonionic polymeric surfactant in kerosene has a foam half-life at 22° C. of at least 10 minutes. In some embodiments, the weight average molecular weight of the nonionic polymeric surfactant is at least 45,000 grams per mole. In some embodiments, the nonionic polymeric surfactant is present in a range from 0.1 percent to 5 percent by weight, based on total weight of the foam. In some embodiments, the method further comprises injecting a plurality of proppant particles into the fracture. In some embodiments, the foam further comprises a gelling agent.

In another aspect, the present invention provides a method of completing a well in a subterranean geological formation penetrated by a well bore, the method comprising:

providing a foam comprising a liquid hydrocarbon and a nonionic polymeric surfactant comprising fluorinated repeating units, wherein the fluorinated repeating units have up to 5 perfluorinated carbon atoms, and wherein a one weight percent solution of the nonionic polymeric surfactant in kerosene has a foam half-life at 22° C. of at least 10 minutes;

introducing the foam into the well bore of the subterranean geological formation; and

carrying out a completion operation in the well bore of the subterranean geological formation. In some embodiments, the completion operation is at least one of gravel packing the well bore, cleaning the well bore, or cementing the well bore.

In some embodiments of the foregoing aspects, the nonionic polymeric surfactant comprises:

at least one divalent unit represented by formula I:

at least one divalent unit represented by formula II:

-   -   wherein         -   Rf is a perfluoroalkyl group having from 3 to 4 carbon             atoms;         -   R and R² are each independently hydrogen or alkyl of 1 to 4             carbon atoms;         -   R¹ is alkyl of 16 to 24 carbon atoms; and         -   n is an integer from 2 to 11.             In some of these embodiments, R¹ is alkyl of 18 to 22 carbon             atoms. In some embodiments, the nonionic polymeric             surfactant comprises the divalent unit represented by             formula I in a range from 45 to 75 weight percent, based on             the total weight of the nonionic polymeric surfactant.

In some embodiments of the foregoing aspects, the liquid hydrocarbon is at least one of kerosene, diesel, gasoline, pentane, hexane, heptane, mineral oil, or a naphthene.

In another aspect, the present invention provides a method of making a nonionic polymeric surfactant, the method comprising:

combining components comprising:

-   -   at least one compound represented by formula:

-   -   at least one compound represented by formula:

-   -   -   wherein         -   Rf is independently a perfluoroalkyl group having from 3 to             4 carbon atoms;         -   R and R² are each independently hydrogen or alkyl of 1 to 4             carbon atoms;         -   R¹ is independently alkyl of 16 to 24 carbon atoms; and         -   n is independently an integer from 2 to 11,

    -   a chain-transfer agent,

    -   a free-radical initiator, and

    -   solvent; and

heating the components at a temperature of up to 70° C.

Methods of treating a subterranean geological formation and completing a well according to the present invention use nonionic polymeric surfactants that typically produce stable hydrocarbon foams (i.e., foams that have a long half-life). In some embodiments of the foregoing aspects, a one weight percent solution of the nonionic polymeric surfactant in kerosene has a foam half-life at 22° C. of at least 12, 14, 16, 18, 20, 22, 24, 26, 28, or even at least 30 minutes. In some embodiments, a one weight percent solution of the nonionic polymeric surfactant in kerosene has a foam half-life at 22° C. of greater than 20 minutes. In some embodiments of methods according to the present invention, the foam is stable under downhole conditions, and in some embodiments, the foam is stable throughout the duration of the method (i.e., the treating or the completing of the subterranean geological formation). Nonionic polymeric surfactants useful in practicing the present invention provide hydrocarbon foams that are typically, and surprisingly, more stable than a nonionic polymeric surfactant containing perfluorobutanesulfonamido groups used previously in drilling fluids and in enhanced oil recovery operations. In some embodiments, nonionic polymeric surfactants useful in practicing the present invention provide hydrocarbon foams that are at least as stable as foams comprising analogous nonionic polymeric surfactants containing perfluorooctanesulfonamido groups.

In this application:

“Alkyl group” and the prefix “alk-” are inclusive of both straight chain and branched chain groups and of cyclic groups. Cyclic groups can be monocyclic or polycyclic and, in some embodiments, have from 3 to 10 ring carbon atoms.

The term “perfluoroalkyl group” includes linear, branched, and/or cyclic alkyl groups in which all C—H bonds are replaced by C—F bonds as well as groups in which hydrogen or chlorine atoms are present instead of fluorine atoms provided that up to one atom of either hydrogen or chlorine is present for every two carbon atoms. In some embodiments of perfluoroalkyl groups, when at least one hydrogen or chlorine is present, the perfluoroalkyl group includes at least one trifluoromethyl group.

The term “hydrocarbon” refers to compounds consisting of carbon and hydrogen and includes linear, branched, and cyclic groups which may be saturated or unsaturated.

The term “nonionic” refers to being free of ionic groups (e.g., salts) or groups (e.g., —CO₂H, —SO₃H, —OSO₃H, —P(═O)(OH)₂) that are readily ionized in water.

The term “foam” refers to a mixture of gas (e.g., nitrogen, carbon dioxide, air, and natural gas) and liquid, which in this application comprises a liquid hydrocarbon.

All numerical ranges are inclusive of their endpoints unless otherwise stated.

DETAILED DESCRIPTION

The stability (i.e., foam half-life) and other properties (e.g., foam expansion) of foams useful in practicing the present invention can be measured using techniques known in the art; (see, e.g., Alm, R. R. et al., Chemical Times & Trends, April, 1986, pp. 40-48). In this application, the foam half-life is determined by placing about 200 mL of a one weight percent solution of the nonionic polymeric surfactant in kerosene in the bowl of a food mixer obtained from Hobart, Troy, Ohio (model N-50) and mixing the solution at 22° C. for three minutes at medium speed (300 rpm) using the wire whisk attachment. The resulting foam is then immediately poured into a 2000-mL graduated cylinder made of “NALGENE” high density polypropylene and having a internal diameter of about 8 centimeters and a height of about 52 centimeters (obtained from VWR International, West Chester, Pa.) to measure the foam expansion and foam half-life. The time necessary for half of the liquid to be drained from the foam (i.e., to provide half of the initial volume of liquid) is measured to provide the foam half-life. Foam expansion refers to the volume achieved after foaming divided by the volume of the liquid before foaming. The foam index is calculated by multiplying the foam expansion by the foam half-life.

Foams useful in practicing the present invention comprise a nonionic polymeric surfactant. In some embodiments, the nonionic polymeric surfactant comprises fluorinated repeating units having 4 (in some embodiments, 3, 2, or even 1) perfluorinated carbon atoms. In some embodiments, nonionic polymeric surfactants useful in practicing the present invention comprise at least one divalent unit represented by formula I:

In some embodiments, nonionic polymeric surfactants useful in practicing the present invention comprise at least one divalent unit represented by formula Ia:

In formula I or Ia, Rf is a perfluoroalkyl group having from 3 to 4 carbon atoms (e.g., perfluoro-n-butyl, perfluoroisobutyl, perfluoro-sec-butyl, perfluoro-tert-butyl, perfluoro-n-propyl, or perfluoroisopropyl). In some embodiments of formula I or Ia, Rf is perfluoro-n-butyl.

In formula I or Ia, R is hydrogen or alkyl of 1 to 4 carbon atoms (e.g., methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, or sec-butyl). In some embodiments of formula I or Ia, R is methyl or ethyl.

In formula I or Ia, n is an integer having a value from 2 to 11 (i.e., 2, 3, 4, 5, 6, 7, 8, 9, 10, or 1).

In some embodiments, nonionic polymeric surfactants useful in practicing the present invention have at least one divalent unit represented by formula Ib:

In some embodiments, nonionic polymeric surfactants useful in practicing the present invention comprise repeating units having pendant alkyl groups of 14 to 24 (in some embodiments, 16 to 24, or even 18 to 22) carbon atoms. In some embodiments, nonionic polymeric surfactants useful in practicing the present invention comprise at least one divalent unit represented by the formula II:

R² is hydrogen or alkyl of 1 to 4 carbon atoms (e.g., methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, or sec-butyl). In some embodiments of formula II, R² is hydrogen. In some embodiments of formula II, R² is methyl.

R¹ is alkyl of 16 to 24 (in some embodiments, 18 to 22) carbon atoms.

In some embodiments, nonionic polymeric surfactants comprising at least one divalent unit represented by formula II wherein R¹ is alkyl of 16 to 24 (or even 18 to 22) carbon atoms provide surprisingly longer-lived foams than nonionic polymeric surfactants comprising at least one divalent unit represented by formula II wherein R¹ is alkyl of less than 14 carbon atoms.

In some embodiments, nonionic polymeric surfactants useful in practicing the present invention comprise at least one divalent unit represented by formula I in a range from 45 to 75 (in some embodiments, from 50 to 70 or even from 55 to 65) weight percent, based on the total weight of the nonionic polymeric surfactant.

In some embodiments, nonionic polymeric surfactants useful in practicing the present invention comprise at least one divalent unit represented by formula Ia in a range from 30 to 65 (in some embodiments, from 35 to 60 or even from 45 to 55) weight percent, based on the total weight of the nonionic polymeric surfactant.

In some embodiments, nonionic polymeric surfactants useful in practicing the present invention comprise at least one divalent unit represented by formula II in a range from 25 to 55 (in some embodiments, from 30 to 50 or even from 35 to 45) weight percent or in a range from 35 to 70 (in some embodiments, from 40 to 65 or even from 45 to 55) weight percent, based on the total weight of the nonionic polymeric surfactant.

In some embodiments of nonionic polymeric surfactants useful in the present invention, divalent groups independently represented by at least one of formula I or Ia and divalent groups independently represented by formula II are randomly copolymerized.

Nonionic polymeric surfactants useful in practicing the present invention may be prepared, for example, by copolymerizing a mixture containing at least first and second monomers typically in the presence of a chain transfer agent and an initiator. By the term “copolymerizing” it is meant forming a polymer or oligomer that includes at least one identifiable structural element due to each of the first and second monomers. Typically, the polymer or oligomer that is formed has a distribution of molecular weights and compositions.

In some embodiments, the first monomer is at least one of a fluorinated free-radically polymerizable monomer represented by formula III, IIIa, or IIIb:

wherein Rf, R, and n are as defined above for the units of formulas I and Ia.

In some embodiments, the second monomer is an aliphatic free-radically polymerizable monomer represented by formula IV:

wherein R¹ and R² are as defined above for the divalent unit of formula II.

Fluorinated free-radically polymerizable monomers of formulas III, IIIa, and IIIb and methods for their preparation, are known in the art; (see, e.g., U.S. Pat. Nos. 2,803,615 (Albrecht et al.) and 6,664,354 (Savu et al.), the disclosures of which, relating to free-radically polymerizable monomers and methods of their preparation, are incorporated herein by reference). Methods described for making nonafluorobutanesulfonamido group-containing structures in the above references can be used to make heptafluoropropanesulfonamido groups by starting with heptafluoropropanesulfonyl fluoride, which can be made, for example, by the methods described in Examples 2 and 3 of U.S. Pat. No. 2,732,398 (Brice et al.), the disclosure of which is incorporated herein by reference.

Compounds of formula IV (e.g., hexadecyl methacrylate, octadecyl methacrylate, stearyl acrylate, behenyl methacrylate) are available, for example, from several chemical suppliers (e.g., Sigma-Aldrich Company, Milwaukee, Wis.; VWR International, West Chester, Pa.; Monomer-Polymer & Dajac Labs, Festerville, Pa.; Avocado Organics, Ward Hill, Mass.; and Ciba Specialty Chemicals, Basel, Switzerland) or may be synthesized by conventional methods. Some compounds of formula IV are available as single isomers (e.g., straight-chain isomer) of single compounds. Other compounds of formula IV are available, for example, as mixtures of isomers (e.g., straight-chain and branched isomers), mixtures of compounds (e.g., hexadecyl acrylate and octadecyl acrylate), and combinations thereof.

In some embodiments, mixtures of more than one first monomer and/or more than one second monomer can be used. In other embodiments, one first monomer and one second monomer can be used.

Polymerization of at least one first monomer and at least one second monomer is typically carried out in the presence of an added free-radical initiator. Free radical initiators such as those widely known and used in the art may be used to initiate polymerization of the components. Examples of free-radical initiators include azo compounds (e.g., 2,2′-azobisisobutyronitrile (AIBN), 2,2′-azobis(2-methylbutyronitrile), or azo-2-cyanovaleric acid), hydroperoxides (e.g., cumene, tert-butyl or tert-amyl hydroperoxide), dialkyl peroxides (e.g., di-tert-butyl or dicumylperoxide), peroxyesters (e.g., tert-butyl perbenzoate or di-tert-butyl peroxyphthalate), diacylperoxides (e.g., benzoyl peroxide or lauryl peroxide). Useful photoinitiators include benzoin ethers (e.g., benzoin methyl ether or benzoin butyl ether); acetophenone derivatives (e.g., 2,2-dimethoxy-2-phenylacetophenone or 2,2-diethoxyacetophenone); and acylphosphine oxide derivatives and acylphosphonate derivatives (e.g., diphenyl-2,4,6-trimethylbenzoylphosphine oxide, isopropoxyphenyl-2,4,6-trimethylbenzoylphosphine oxide, or dimethyl pivaloylphosphonate). When heated or photolyzed such free-radical initiators fragment to generate free radicals which add to ethylenically unsaturated bonds and initiate polymerization.

Polymerization reactions may be carried out in any solvent suitable for organic free-radical polymerizations. The components may be present in the solvent at any suitable concentration, (e.g., from about 5 percent to about 90 percent by weight based on the total weight of the reaction mixture). Illustrative examples of suitable solvents include aliphatic and alicyclic hydrocarbons (e.g., hexane, heptane, and cyclohexane), aromatic solvents (e.g., benzene, toluene, and xylene), ethers (e.g., diethyl ether, glyme, diglyme, and diisopropyl ether), esters (e.g., ethyl acetate and butyl acetate), alcohols (e.g., ethanol and isopropyl alcohol), ketones (e.g., acetone, methyl ethyl ketone, and methyl isobutyl ketone), sulfoxides (e.g., dimethyl sulfoxide), amides (e.g., N,N-dimethylformamide and N,N-dimethylacetamide), halogenated solvents (e.g., methylchloroform, 1,1,2-trichloro-1,2,2-trifluoroethane, trichloroethylene, and trifluorotoluene), and mixtures thereof.

Polymerization can be carried out at any temperature suitable for conducting an organic free-radical reaction. Temperature and solvent for a particular use can be selected by those skilled in the art based on considerations such as the solubility of reagents, temperature required for the use of a particular initiator, and desired molecular weight. While it is not practical to enumerate a particular temperature suitable for all initiators and all solvents, generally suitable temperatures are in a range from about 30° C. to about 200° C. (in some embodiments, from about 40° C. to about 100° C., or even from about 50° C. to about 80° C.). For some embodiments of a method of making a nonionic polymeric surfactant according to the present invention, the components may be heated at a temperature in a range from about 30° C. to about 70° C. (in some embodiments, from about 40° C. to about 70° C., or even from about 50° C. to about 70° C.).

Free-radical polymerizations may be carried out in the presence of chain transfer agents. Typical chain transfer agents that may be used in the preparation of nonionic polymeric surfactants useful in practicing the present invention include hydroxyl-substituted mercaptans (e.g., 2-mercaptoethanol, 3-mercapto-2-butanol, 3-mercapto-2-propanol, 3-mercapto-1-propanol, and 3-mercapto-1,2-propanediol (i.e., thioglycerol)); amino-substituted mercaptans (e.g., 2-mercaptoethylamine); difunctional mercaptans (e.g., di(2-mercaptoethyl)sulfide); and aliphatic mercaptans (e.g., octylmercaptan and dodecylmercaptan).

Adjusting, for example, the concentration and activity of the initiator, the concentration of each monomer, the temperature, the concentration of the chain transfer agent, and the solvent using techniques known in the art can control the molecular weight of a polyacrylate copolymer.

In some embodiments, nonionic polymeric surfactants useful in practicing and/or prepared according to the present invention have a weight average molecular weight of at least 45,000 (in some embodiments, at least 50,000, 55,000, 60,000, 65,000, 70,000, 75,000, 80,000, 85,000, 90,000, 95,000, 100,000, 105,000, 110,000, 115,000, 120,000, 125,000, 130,000, 135,000, or even at least 140,000) grams per mole. In some embodiments, nonionic polymeric surfactants useful in practicing the present invention have a weight average molecular weight of up to 250,000 (in some embodiments, up to 245,000, 240,000, 235,000, 230,000, 225,000, 220,000, 215,000, 210,000, 205,000, 200,000, 195,000, 190,000, 185,000, 180,000, 175,000, 170,000, 165,000, or even up to 160,000) grams per mole. Surprisingly, in some embodiments, nonionic polymeric surfactants having a weight average molecular weight of at least 45,000 grams per mole have been observed to provide at least one of longer-lived foams or a higher foam expansion than nonionic polymeric surfactants having a weight average molecular weight of up to 20,000 grams per mole. The nonionic polymeric surfactants typically have a distribution of molecular weights and compositions. Weight average molecular weights can be measured, for example, by gel permeation chromatography (i.e., size exclusion chromatography) using techniques known in the art.

Typically, for methods of treating a subterranean geological formation and completing a well according to the present invention the foam includes from at least 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, 0.1, 0.15, 0.2, 0.25, 0.5, 1, 1.5, 2, 3, 4, or 5 percent by weight, up to 5, 6, 7, 8, 9, or 10 percent by weight of the nonionic polymeric surfactant, based on the total weight of the foam. For example, the amount of the nonionic polymeric surfactant in the foams may be in a range of from 0.01 to 10, 0.1 to 10, 0.1 to 5, 1 to 10, or even in a range from 1 to 5 percent by weight, based on the total weight of the foam. In some embodiments, the nonionic polymeric surfactant is present in a range from 0.3 to 0.5 percent by weight, based on the total weight of the foam. Lower and higher amounts of the nonionic polymeric surfactant in the compositions may also be used, and may be desirable for some applications.

Foams used in methods of treating a subterranean geological formation and completing a well according to the present invention comprise a liquid hydrocarbon. Liquid hydrocarbons suitable for practicing the present invention include crude oil; refined hydrocarbons (e.g., gasoline, kerosene, and diesel); paraffinic and isoparaffinic hydrocarbons (e.g., pentanes, hexanes, heptanes, higher alkanes, and isoparaffinic solvents obtained from Total Fina, Paris, France, under trade designations “ISANE IP 130” and “ISANE IP 175” and from Exxon Mobil Chemicals, Houston, Tex., under the trade designation “ISOPAR”); mineral oil; ligroin; naphthenes; aromatics (e.g., xylenes and toluene); natural gas condensates; and combinations (either miscible or immiscible) thereof. In some embodiments, the liquid hydrocarbon is kerosene. In some embodiments, the liquid hydrocarbon is diesel. Liquid hydrocarbons suitable for use as fracturing fluids can be obtained, for example, from SynOil, Calgary, Alberta, Canada under the trade designations “PLATINUM”, “TG-740”, “SF-770”, “SF-800”, “SF-830”, and “SF-840”.

Forming gas bubbles (e.g., nitrogen, carbon dioxide, and air) in a composition comprising a liquid hydrocarbon and a nonionic fluorinated polymeric surfactant useful in practicing the present invention can be carried out using a variety of mechanisms (e.g., mechanical and chemical mechanisms). Useful mechanical foaming mechanisms include agitating (e.g., shaking, stirring, and whipping) the composition, injecting gas into the composition (e.g., inserting a nozzle beneath the surface of the composition and blowing gas into the composition) and combinations thereof. Useful chemical foaming mechanisms include producing gas in situ through a chemical reaction, decomposition of a component of the composition (e.g., a component that liberates gas upon thermal decomposition), evaporating a component of the composition (e.g., a liquid gas and volatilizing a gas in the composition by decreasing the pressure on the composition or heating the composition). Mixing gas bubbles into liquid hydrocarbons to form foams, for example, at a well site (or even at the well head) can be carried out using one of several methods known in the art. Such methods include those described in U.S. Pat. Nos. 3,463,231 (Hutchison et al.) and 3,819,519 (Sharman et al.), the disclosures of which, relating to methods of generating foams, are incorporated herein by reference. Foams useful in practicing the present invention typically comprise gas at volume fractions ranging from 10% to 90% of the total foam volume.

Techniques for treating subterranean geological formations comprising hydrocarbons in order to open at least one fracture therein are known in the art. A fracturing fluid (e.g., a foam) is typically injected at a high pressure that exceeds the rock strength and opens a fracture in the rock. A variety of pumping systems (e.g., positive displacement and centrifugal pumps) employing a variety of drivers (e.g., motors, turbines, and generators) may be used. Methods according to the present invention may be used to enhance extraction of hydrocarbons (e.g., oil and gas), from naturally occurring or man-made reservoirs.

Techniques for completing a subterranean geological formation penetrated by a well bore (e.g., gravel packing the well bore, cleaning the well bore, and cementing the well bore) by introducing a foam into the subterranean geological formation are known in the art (see, e.g., U.S. Pat. No. 7,066,262 (Funkhouser), the disclosure of which is incorporated herein by reference). The terms “well” and “well bore” include a producing well, a non-producing well, an injection well, a fluid disposal well, an experimental well, and an exploratory well. Wells and well bores may be vertical, horizontal, deviated some angle between vertical and horizontal, and combinations thereof (e.g., a vertical well with a non-vertical component). The term “introducing” includes pumping, injecting, pouring, releasing, displacing, spotting, circulating, and otherwise placing a foam within a well, well bore, or subterranean geological formation using any suitable manner known in the art.

In some embodiments, methods of treating a subterranean geological formation comprising hydrocarbons according to the present invention further comprise injecting a plurality of proppant particles into the fracture formed by injecting a foam into the formation at a rate and pressure sufficient to open at least one fracture therein. Proppant particles so injected prevent the formed fractures from closing, thereby maintaining conductive channels through which hydrocarbons in the formation can flow. Techniques for injecting proppant particles into fractured subterranean geological formations are known in the art. In some embodiments, injecting the plurality of proppant particles and injecting the foam are carried out simultaneously. The proppant particles may be combined with the foam prior to injection into the formation. In some embodiments, injecting the plurality of proppant particles is carried out after injecting the foam.

In some embodiments of methods of completing a subterranean geological formation penetrated by a well bore, the foam further comprises a plurality of gravel particles. Foams containing suspended gravel particles can be used to deliver the gravel particles to a desired area in a well bore (e.g., near unconsolidated or weakly consolidated formation sand) to form a gravel pack to enhance sand control.

Suitable proppant and gravel particles useful in practicing the present invention include graded walnut shells, other graded nut shells, resin-coated walnut shells, other resin-coated nut shells, graded sand, resin-coated sand, sintered bauxite, particulate ceramic materials, glass beads, and particulate thermoplastic materials. Sand particles are available, for example, from Badger Mining Corp., Berlin, Wis.; Borden Chemical, Columbus, Ohio; Fairmont Minerals, Chardon, Ohio. Thermoplastic particles are available, for example, from the Dow Chemical Company, Midland, Mich.; and BJ Services, Houston, Tex. Clay-based particles are available, for example, from CarboCeramics, Irving, Tex.; and Saint-Gobain, Courbevoie, France. Sintered bauxite ceramic particles are available, for example, from Borovichi Refractories, Borovichi, Russia; 3M Company, St. Paul, Minn.; CarboCeramics; and Saint Gobain. Glass beads are available, for example, from Diversified Industries, Sidney, British Columbia, Canada; and 3M Company. The size of the particles employed may depend, for example, on the characteristics of the subterranean formation. Generally, the sizes of suitable particulates may vary in the range of from about 2 to about 200 mesh (U.S. Sieve Series scale).

In some embodiments, foams useful in practicing the present invention further comprise a gelling agent (e.g., a phosphoric acid ester). In some of these embodiments, the foams further comprise an activator (e.g., a source of polyvalent metal ions) for the gelling agent. Typically, in embodiments where gelling agents are used, liquid hydrocarbons useful in practicing the present invention are combined with a gelling agent (e.g., a phosphoric acid ester), an activator (e.g., ferric sulfate, ferric chloride, aluminum chloride, sodium aluminate, and aluminum isopropoxide), and a nonionic polymeric surfactant, and the resulting mixture is converted to a foam, which is injected into the subterranean geological formation. Gelling agents and activators useful in practicing the present invention are described, for example, in U.S. Pat. Nos. 4,622,155 (Harris et al.) and 5,846,915 (Smith et al.), the disclosures of which are incorporated herein by reference. In some embodiments wherein gelling agents are used, a suitable breaker may be included in or added to the foam so that the viscosity of the treatment foam may eventually be reduced, for example, to recover it from the subterranean formation at a desired time. Suitable breakers include, for example, those described in U.S. Pat. No. 7,066,262 (Funkhouser), the disclosure of which is incorporated herein by reference.

Embodiments and advantages of this invention are further illustrated by the following non-limiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details should not be construed to unduly limit this invention.

Unless otherwise noted, all parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight.

EXAMPLES Weight Average Molecular Weight Determination

The weight average molecular weights of Examples 1, 3, and 18 were determined by comparison to linear polystyrene polymer standards using gel permeation chromatography (GPC). The GPC measurements were carried out on a Waters Alliance 2695 system (obtained from Waters Corporation, Milford, Mass.) using four 300 millimeter (mm) by 7.8 mm linear columns of 5 micrometer styrene divinylbenzene copolymer particles (obtained from Polymer Laboratories, Shropshire, UK, under the trade designation “PLGEL”) with pore sizes of 10,000, 1000, 500, and 100 angstroms. A refractive index detector from Waters Corporation (model 410) was used at 40° C. A 50-milligram (mg) sample of oligomer at 40% solids in ethyl acetate was diluted with 10 milliliters (mL) of tetrahydrofuran (inhibited with 250 ppm of BHT) and filtered through a 0.45 micrometer syringe filter. A sample volume of 100 microliters was injected onto the column, and the column temperature was 40° C. A flow rate of 1 mL/minute was used, and the mobile phase was tetrahydrofuran. Molecular weight calibration was performed using narrow dispersity polystyrene standards with peak average molecular weights ranging from 3.8×10⁵ grams per mole to 580 grams per mole. Calibration and molecular weight distribution calculations were performed using suitable GPC software using a third order polynomial fit for the molecular weight calibration curve. Each reported result is an average of duplicate injections.

Example 1

Under vacuum (300 mmHg (4×10⁴ Pa)), 340 pounds (154 kilograms (kg)) of a 50% solution of N-methylperfluorobutanesulfonamidoethyl methacrylate (MeFBSEMA) in ethyl acetate was added to a 75-gallon (284-liter) stainless steel reactor with a jacket temperature set to 70° F. (21° C.), and the solution was stirred at 80 rpm. The vacuum was restored, and 113 pounds (51 kg) of stearyl methacrylate (obtained from Rohm & Haas, Philadelphia, Pa.) was added to the reactor. The vacuum was restored, and a pre-mixed solution of 276 grams (g) of thioglycerol (obtained from Evans Chemetics, Iselin, N.J.) and 2 pounds (0.9 kg) of ethyl acetate were added to the reactor followed by 229 pounds (104 kg) of ethyl acetate. The reactor was placed under nitrogen pressure (50 psi (3.4×10⁵ Pa)), and the reactor jacket temperature was raised to 149° F. (65° C.). With continued stirring at 80 rpm, a pre-mixed solution of 5.7 pounds (2.6 kg) of tert-butyl peroxy-2-ethylhexanoate (obtained from Atofina, Philadelphia, Pa., as a 50% solution in mineral spirits under the trade designation “LUPEROX 26M50”) and 4 pounds (1.8 kg) of ethyl acetate was added. The reaction mixture was stirred and heated at 149° F. (65° C.) for about 27 hours, allowed to cool to about 90° F. (32° C.), and drained into two 55-gallon (208-liter) drums and one 5-gallon (19-liter) pail. The weight of the resulting product solution was 645 pounds (292 kg). A sample was heated for 1 hour and 105° C., conditions under which the monomers and solvents were completely volatile, and was determined to be 41% solids. The weight average molecular weight was determined to be 1.36×10⁵ grams per mole (and the number average molecular weight 4.0×10⁴ grams per mole) using the test method described above.

MeFBSEMA was made according to the method of U.S. Pat. No. 6,664,354 (Savu), Example 2, Parts A and B, incorporated herein by reference, except using 3420 kg of N-methylperfluorobutanesulfonamidoethanol, 1.6 kg of phenothiazine, 2.7 kg of methoxyhydroquinone, 1400 kg of heptane, 980 kg of methacrylic acid (instead of acrylic acid), 63 kg of methanesulfonic acid (instead of triflic acid), and 7590 kg of water in Part B.

Test for Foam Stability

A 1% by weight solution of Example 1 was prepared by dilution of the 41% solids solution in ethyl acetate with kerosene (obtained from Alfa Aesar, Ward Hill, Mass.) to make 188 mL of solution. The solution was placed in the bowl of a food mixer obtained from Hobart, Troy, Ohio (model N-50) equipped with a wire whisk stirrer, and the solution was stirred for 3 minutes at 300 rpm at room temperature (22° C.). The resulting foam was immediately transferred to a 2000 mL graduated cylinder made of “NALGENE” high density polypropylene and having a internal diameter of about 8 centimeters and a height of about 52 centimeters (obtained from VWR International, West Chester, Pa.). The volume of foam was measured in mL, and the foam expansion (i.e., the foam volume divided by 188) was recorded. The foam volume was observed over time, and the time at which 94 mL of liquid were present (i.e., the foam half-life) was recorded. The foam index (i.e., the product of the foam expansion and the foam half-life) was calculated. The foam half-life, foam volume, and foam index are reported in Table 1, below.

TABLE 1 Fluorinated Non- Foam Half Foam Monomer fluorinated Life, volume, Foam (g) Monomer (g) minutes mL Index Example 1 MeFBSEMA Stearyl 25 1380 183 (77,000)    Methacrylate (51,000)    Example 2 MeFBSEA Octadecyl 55 1500 438 (50) Methacrylate (50) Example 3 MeFBSEA Stearyl   51.5 1450 389 (250)  Methacrylate (250)  Example 4 MeFBSEA Stearyl 43 1450 331 (50) Acrylate (50) Example 5 MeFBSEA Octadecyl 41 1550 337 (40) Methacrylate (60) Example 6 MeFBSEA Octadecyl   28.5 1300 197 (60) Methacrylate (40) Example 7 MeFBSEA Behenyl   40.5 1350 290 (40) Methacrylate (60) Example 8 MeFBSEA Behenyl   34.5 1150 211 (50) Methacrylate (50) Example 9 MeFBSEMA Octadecyl   23.5 1300 162 (55) Methacrylate (45) Example MeFBSEMA Octadecyl 23 1360 166 10 (60) Methacrylate (40) Example MeFBSEMA Octadecyl 24 1300 165 11 (65) Methacrylate (35) Example MeFBSEMA Behenyl   30.5 1275 207 12 (412)  Methacrylate (275)  Example MeFBSEMA Octadecyl   16.5 1060  93 13 (70) Methacrylate (30) Example MeFBSEA Decyl 13 1250  86 14 (60) Methacrylate (40) Example MeFBSEA Dodecyl   17.5 1350   125.7 15 (70) Methacrylate (30) Example FBMA Octadecyl   12.5 2100   139.6 16 (60) Methacrylate (40) Example MeFBSEMA Octadecyl   14.5 1100  85 17 (50) Methacrylate (50) Example MeFBSEA Octadecyl  13^(a)  1570^(a)  109^(a) 18 (250)  Methacrylate (250)  Illustrative FBMA Hexadecyl   0.5 1050    2.75 Example 1 (50) Methacrylate (50) Illustrative MeFBSEMA Octadecyl  2  960  10 Example 2 (40) Methacrylate (60) Illustrative FBMA Stearyl  9 1600   76.5 Example 3 (60) Acrylate (40) Illustrative MeFBSEMA Decyl not not not Example 4 (60) Methacrylate soluble^(b) soluble^(b) soluble^(b) (40) Illustrative MeFBSEMA Dodecyl   5.5  940  28 Example 5 (60) Methacrylate (40) C.E.^(c) A FOMA Dodecyl    0.25  600    0.8 (30) Methacrylate (70) C.E.^(c) B EtFOSEA Dodecyl 19 1500 152 (60) Methacrylate (40) C.E.^(c) C NFA Dodecyl    0.25  500    0.66 (10) Methacrylate   (6.7) C.E.^(c) D NFA Dodecyl  0  500  0 (10) Methacrylate (30) C.E.^(c) E NFMA Dodecyl   8.5 2250 102 (10) Methacrylate (23) C.E.^(c) F NFMA Dodecyl  9 1400  67 (10) Methacrylate   (6.7) ^(a)Average of two measurements. ^(b)The polymer was not soluble in kerosene; therefore, it was not possible to prepare a foam. ^(c)Comparative Example.

Example 2

Under a flow of nitrogen, 50 g of N-methylperfluorobutanesulfonamidoethyl acrylate (MeFBSEA), 50 g of octadecyl methacrylate (obtained from TCI, Tokyo, Japan, at 95% purity), 0.2 g of thioglycerol (obtained from Sigma-Aldrich, Milwaukee, Wis.), and 143 g of ethyl acetate were added to a 1-L flask equipped with an overhead stirrer, a thermocouple, and a reflux condenser. After the additions, the contents of the flask were kept under slightly positive nitrogen pressure. The temperature set point was raised to 65° C. using a J-Kem temperature controller (obtained from VWR International, West Chester, Pa.), and 2.0 g of a 50/50 mixture of mineral spirits/tert-butyl peroxy-2-ethylhexanoate (“LUPEROX 26M50”) was added. The reaction was observed for 15 minutes, and then the temperature set point was raised to 70° C. using the temperature controller. The reaction was heated at 70° C. overnight and allowed to cool to room temperature. The test for foam stability was carried out as described in Example 1, and the results are reported in Table 1, above.

MeFBSEA was made according to the method of U.S. Pat. No. 6,664,354 (Savu), Example 2, Parts A and B, incorporated herein by reference, except using 4270 kg of N-methylperfluorobutanesulfonamidoethanol, 1.6 kg of phenothiazine, 2.7 kg of methoxyhydroquinone, 1590 kg of heptane, 1030 kg of acrylic acid, 89 kg of methanesulfonic acid (instead of triflic acid), and 7590 kg of water in Part B.

Example 3

Example 3 was prepared using the method of Example 2 except that 250 g of MeFBSEA, 250 g of stearyl methacrylate (obtained from Sigma-Aldrich, Milwaukee, Wis.), 1.0 g of thioglycerol, 10.0 g of a 50/50 mixture of mineral spirits/tert-butyl peroxy-2-ethylhexanoate (“LUPEROX 26M50”), and 715 g of ethyl acetate were used. The weight average molecular weight was determined to be 1.28×10⁵ grams per mole (and the number average molecular weight 6.8×10⁴ grams per mole) using the test method described above. The test for foam stability was carried out as described in Example 1, and the results are reported in Table 1, above.

Examples 4-17 Illustrative Examples 1-5 and Comparative Examples A-B

Examples 4-17, Illustrative Examples 1-5, and Comparative Examples A-B were prepared and tested using the methods of Example 2 except using the monomers and amounts shown in Table 1, above.

Stearyl Acrylate was obtained from VWR International. Behenyl Methacrylate was obtained from Ciba Specialty Chemicals, Basel, Switzerland, under the trade designation “CIBA AGEFLEX FM22”. Decyl methacrylate and hexadecyl methacrylate were obtained from Monomer-Polymer & Dajac Labs, Feasterville, Pa. Dodecyl methacrylate was obtained from Avocado Organics, Ward Hill, Mass. 2,2,3,3,4,4,4-Heptafluorobutyl 2-methylacrylate (FBMA) was prepared as described in paragraph 47 of EP1311637 (Savu et al.), published Apr. 5, 2006, incorporated herein by reference. 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-Pentadecafluorooctyl 2-methylacrylate (FOMA) was obtained from 3M Company, St. Paul, Minn., under the designation “L-9179”. N-Ethylperfluorooctanesulfonamidoethyl acrylate (EtFOSEA) was obtained from 3M Company under the trade designation “FX-13”.

The test for foam stability was carried out as described in Example 1. The results from the foam testing of Examples 4-17, Illustrative Examples 1-5, and Comparative Examples A-B are given in Table 1, above.

Comparative Example C

Under a flow of nitrogen, 10 g of 3,3,4,4,5,5,6,6,6-nonafluorohexyl acrylate (NFA) (obtained from Daikin Chemical Sales, Osaka, Japan), 6.7 g of dodecyl methacrylate (obtained from Avocado Organics), 0.03 g of thioglycerol, and 33 g of ethyl acetate were added to a 1-L flask equipped with an overhead stirrer, a thermocouple, and a reflux condenser. After the additions, the contents of the flask were kept under slightly positive nitrogen pressure. The temperature set point was raised to 65° C. using a J-Kem temperature controller (obtained from VWR International), and 0.33 g of a 50/50 mixture of mineral spirits/tert-butyl peroxy-2-ethylhexanoate (“LUPEROX 26M50”) was added. The reaction was observed for 15 minutes, and then the temperature set point was raised to 70° C. using the temperature controller. The reaction was heated at 70° C. overnight and allowed to cool to room temperature. The test for foam stability was carried out as described in Example 1, and the results are reported in Table 1, above.

Comparative Examples D-F

Comparative Examples D-F were prepared and tested using the methods of Comparative Example C, except using the monomers and amounts shown in Table 1, above. 3,3,4,4,5,5,6,6,6-Nonafluorohexyl 2-methylacrylate (NFMA) was obtained from Indofine Chemical Co., Hillsborough, N.J.

Example 18

Example 18 was prepared and tested using the methods of Example 3, except the polymerization was carried out in hexane. The weight average molecular weight of the resulting polymer was determined to be 8.9×10⁴ grams per mole (and the number average molecular weight 5.7×10⁴ grams per mole) using the test method described above. The foam characteristics are provided in Table 1, above.

Comparative Example G

Under a flow of nitrogen, 840 g of MeFBSEMA, 560 g of stearyl methacrylate (obtained from Sigma-Aldrich), 14.0 g of thioglycerol, and 2000 g of ethyl acetate were added to a 5-L flask equipped with an overhead stirrer, a thermocouple, and a reflux condenser. After the additions, the contents of the flask were kept under slightly positive nitrogen pressure. The temperature set point was raised to 73° C. using a J-Kem temperature controller (obtained from VWR International), and 84 g of a 50/50 mixture of mineral spirits/tert-butyl peroxy-2-ethylhexanoate (“LUPEROX 26M50”) was added. The reaction was observed for 15 minutes, and then the temperature set point was raised to 78° C. using the temperature controller. The reaction was heated at 78° C. for 6 hours and 20 minutes and allowed to cool to room temperature. The weight average molecular weight of the resulting polymer was determined to be 1.5×10⁴ grams per mole (and the number average molecular weight 9.1×10³ grams per mole) using the test method described above except 125 mg of sample were dissolved in tetrahydrofuran, the column was at room temperature, an evaporative light scattering detector (obtained from Polymer Laboratories) was used, and the molecular weight calibration was performed using narrow dispersity polystyrene standards with peak average molecular weights ranging from 1.1×10⁶ grams per mole to 168 grams per mole. The test for foam stability was carried out as described in Example 1. The foam volume was 1120 mL, the foam half-life was 8.5 minutes, and the foam index was 51.

Comparative Example H

A 1% by weight solution of a nonionic polymeric surfactant comprising fluorinated repeating units having 8 perfluorinated carbon atoms (obtained from 3M Company, St. Paul, Minn., as a 50% solution under the trade designation “FC-740”) was prepared and foamed according to the method of Example 1. The foam volume was 1660 mL, the foam half-life was 32 minutes, and the foam index was 282.

Comparative Example I

Comparative Example I was prepared using the method of Example 2, except that 60 g of MeFBSEMA, 20 g of octadecyl methacrylate, and 20 g of an acrylate monomer prepared from a methoxy-terminated polyethylene oxide alcohol, obtained from Union Carbide, Danbury, Conn. under the trade designation “CARBOWAX 750”, using the procedure described in Example 17 of U.S. Pat. No. 3,728,151 (Sherman et al.), the disclosure of which is incorporated herein by reference. The polymer was not soluble in kerosene; therefore, it was not possible to prepare a foam.

Comparative Example J

Comparative Example J was prepared and tested using the methods of Example 2 except that 55 g of MeFBSEMA, 40 g of octadecyl methacrylate, and 5 g of acrylic acid (obtained from Sigma-Aldrich) were used in the preparation. The test for foam stability was carried out as described in Example 1. The foam volume was 1240 mL, the foam half-life was 4.5 minutes, and the foam index was 29.9.

Example 19

A mason jar was charged with 100 g of automotive grade diesel (obtained from Sunoco Service Station, London, Ontario). Surfactant as prepared in Example 1 was added to make a 0.5% solution of surfactant in diesel. The jar was capped and shaken by hand for 30 seconds. The jars were visually inspected at 5 seconds, 30 seconds, 1 minute, 5 minute, 15 minutes, 30 minutes, and 60 minutes, and foam was observed to be present at each inspection.

Example 20

Example 20 was carried out as described in Example 19, except that a 0.3% solution of surfactant was prepared. Foam was observed to be present at each inspection.

Example 21

Example 21 was carried out as described in Example 19, except that a 0.1% solution of surfactant was prepared. Foam was observed to be present at 5 seconds, 30 seconds, 1 minute, 5 minute, and 15 minutes. No foam was observed at 30 minutes.

Example 22

Example 22 was prepared according to the method of Comparative Example G, except that the temperature of the reaction mixture was raised to 60° C. prior to the addition of the tert-butyl peroxy-2-ethylhexanoate “LUPEROX 26M50” initiator, and following the addition of the initiator, the reaction was stirred at 70° C. for 18 hours. The weight average molecular weight was determined to be 1.6×10⁴ grams per mole (and the number average molecular weight 1.0×10⁴ grams per mole) using the test method described above. The test for foam stability was carried out as described in Example 1. The foam height was 1120, the foam half-life was 20 minutes, and the foam index was 119.

Example 23

Example 23 was prepared according to the method of Example 1, except that 2520 g of MeFBSEMA, 1680 g stearyl methacrylate, 9 g thioglycerol, and 5940 g ethyl acetate were added to a 22-liter reactor prior to the addition of 85 g of the initiator “LUPEROX 26M50” in 60 g of ethyl acetate. The weight average molecular weight was determined to be 5.3×10⁴ grams per mole (and the number average molecular weight 1.6×10⁴ grams per mole) using the test method described above. The test for foam stability was carried out as described in Example 1. The foam height was 1290, the foam half-life was 25 minutes, and the foam index was 172.

Examples 24 to 27

Examples 24 to 27 were prepared according to the method of Example 2 except using the monomers and amounts shown in Table 2, below, and adding an additional 122 g of ethyl acetate at the end of the reaction time before cooling to room temperature. The results from the foam testing of Examples 24 to 27 according to the method of Example 1 are given in Table 2, below.

TABLE 2 Non- Non- Fluorinated fluorinated fluorinated Foam Foam Monomer Monomer Monomer Half Life, volume, (g) (g) (g) minutes mL Foam Index Example MeFBSEA Stearyl Behenyl 15 1360 115 24 (50) Methacrylate Methacrylate (40) (10) Example MeFBSEA Stearyl Behenyl 33 1500 263 25 (56) Methacrylate Methacrylate (22) (22) Example MeFBSEA Stearyl Behenyl 37 1500 295 26 (50) Methacrylate Methacrylate (25) (25) Example MeFBSEA Stearyl Behenyl 50 1500 402 27 (50) Methacrylate Methacrylate (10) (40)

Various modifications and alterations of this invention may be made by those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth herein. 

1. A method of completing a well in a subterranean geological formation penetrated by a well bore, the method comprising: providing a foam comprising a liquid hydrocarbon and a nonionic polymeric surfactant comprising fluorinated repeating units, wherein the fluorinated repeating units have up to 5 perfluorinated carbon atoms, and wherein a one weight percent solution of the nonionic polymeric surfactant in kerosene has a foam half-life at 22° C. of at least 10 minutes; introducing the foam into the well bore of the subterranean geological formation; and carrying out a completion operation in the well bore of the subterranean geological formation.
 2. The method of claim 1, wherein the completion operation is at least one of gravel packing the well bore, cleaning the well bore, or cementing the well bore.
 3. The method of claim 1, wherein the nonionic polymeric surfactant comprises: at least one divalent unit represented by formula I:

at least one divalent unit represented by formula II:

wherein Rf is a perfluoroalkyl group having from 3 to 4 carbon atoms; R and R² are each independently hydrogen or alkyl of 1 to 4 carbon atoms; R¹ is alkyl of 16 to 24 carbon atoms; and n is an integer from 2 to
 11. 4. The method of claim 3, wherein R¹ is alkyl of 18 to 22 carbon atoms.
 5. The method of claim 3, wherein the nonionic polymeric surfactant comprises the divalent unit represented by formula I in a range from 45 to 75 weight percent, based on the total weight of the nonionic polymeric surfactant.
 6. The method of claim 3, wherein the weight average molecular weight of the nonionic polymeric surfactant is at least 45,000 grams per mole.
 7. The method of claim 1, wherein a one weight percent solution of the nonionic polymeric surfactant in kerosene has a foam half-life at 22° C. of at least 20 minutes.
 8. The method of claim 1, wherein the nonionic polymeric surfactant is present in a range from 0.1 percent to 5 percent by weight, based on total weight of the foam.
 9. The method of claim 1, wherein the liquid hydrocarbon is at least one of kerosene, diesel, gasoline, pentane, hexane, heptane, mineral oil, or a naphthene.
 10. The method of claim 1, wherein the foam further comprises a plurality of gravel particles.
 11. A method of making a nonionic polymeric surfactant, the method comprising: combining components comprising: at least one compound represented by formula:

at least one compound represented by formula:

wherein Rf is independently a perfluoroalkyl group having from 3 to 4 carbon atoms; R and R² are each independently hydrogen or alkyl of 1 to 4 carbon atoms; R¹ is independently alkyl of 16 to 24 carbon atoms; and n is independently an integer from 2 to 11, a chain-transfer agent, a free-radical initiator, and a solvent; and heating the components at a temperature of up to 70° C.
 12. A method of treating a subterranean geological formation bearing hydrocarbons, the method comprising: injecting a foam into a subterranean geological formation bearing hydrocarbons at a rate and pressure sufficient to open at least one fracture therein, wherein the foam comprises a liquid hydrocarbon and a nonionic polymeric surfactant comprising fluorinated repeating units, wherein the fluorinated repeating units have up to 5 perfluorinated carbon atoms, and wherein a one weight percent solution of the nonionic polymeric surfactant in kerosene has a foam half-life at 22° C. of at least 10 minutes.
 13. The method of claim 12, wherein the nonionic polymeric surfactant comprises: at least one divalent unit represented by formula I:

at least one divalent unit represented by formula II:

wherein Rf is a perfluoroalkyl group having from 3 to 4 carbon atoms; R and R² are each independently hydrogen or alkyl of 1 to 4 carbon atoms; R¹ is alkyl of 16 to 24 carbon atoms; and n is an integer from 2 to
 11. 14. The method of claim 13, wherein R¹ is alkyl of 18 to 22 carbon atoms.
 15. The method of claim 13, wherein the nonionic polymeric surfactant comprises the divalent unit represented by formula I in a range from 45 to 75 weight percent, based on the total weight of the nonionic polymeric surfactant.
 16. The method of claim 13, wherein the weight average molecular weight of the nonionic polymeric surfactant is at least 45,000 grams per mole.
 17. The method of claim 12, wherein the liquid hydrocarbon is at least one of kerosene, diesel, gasoline, pentane, hexane, heptane, mineral oil, or a naphthene.
 18. The method of claim 12, wherein a one weight percent solution of the nonionic polymeric surfactant in kerosene has a foam half-life at 22° C. of at least 20 minutes.
 19. The method of claim 12, further comprising injecting a plurality of proppant particles into the fracture.
 20. The method of claim 19, wherein the foam further comprises a gelling agent. 